• Korean Journal of Materials Research
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• v.12 no.12
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• pp.947-954
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• 2002

HCl concentration and reaction time are the decisive factors in determining the structure of precipitates in the process of synthesis of $TiO_2$ particles from aqueous $TiOCl_2$ solution by precipitation and the volumetric proportion of brookite phase in $TiO_2$ particles can be controlled by these two factors. As reaction rate increases with increase of reaction temperature, the reaction time, at which maximum volumetric proportion of brookite phase in $TiO_2$ particles was obtained, was reduced. The brookite was transformed directly to rutile phase with only increase of reaction time. And precipitation was delayed with increase of HCl concentration because the amount of $H_2$O, which is necessary source of oxygen for conversion of $Ti^{+4}$ to $TiO_2$, was relatively reduced with increase of that. Brookite in the mixture phase powder was finally transformed to rutile phase via anatase through heat-treatment.

• Bulletin of the Korean Chemical Society
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• v.30 no.2
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• pp.402-404
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• 2009

The band structures and the densities of states at the Fermi energy for rutile, anatase and brookite phases are investigated along with the structure-photocatlaytic relationship by using DFT method. Bands are less dispersive in anatase phase than in rutile phase, and they are almost flat in brookite phase. As a result, the DOS value near the Fermi energy for brookite is highest among three types of $TiO_{2}$, which means that the numbers of electrons near the Fermi energy are largest in brookite. The calculation shows that brookite phase may exhibit highest photocatalytic efficiency among three types of $TiO_{2}$.

• Journal of the Korean Ceramic Society
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• v.42 no.7 s.278
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• pp.461-468
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• 2005

Transparent TiO$_{2}$ sols were prepared by hydrothermal synthesis to heat Ti precursor solutions, from Ti hydroxides obtained with neutralizing aqueous TiOCl$_{2}$ solutions having various concentrations of NaCI by aqueous NaOH solution, in the autoclave at 120$^{\circ}C$ The photocatalytic abilities of glass beads coated with the sol for gaseous benzene were evaluated. As a result, it was found that due to the increase of brookite phase in TiO$_{2}$ by controlling the concentration of Na ion the optical absorption of TiO$_{2}$ increases toward long wavelength but that in the area of short wavelength becomes relatively low and consequently the photocatalytic performance of TiO$_{2}$ thin film for benzene gas rather decreases, compared to that of composite film of anatase and brookite phases. These results suggest that in order for coated TiO$_{2}$ thin film to have high dissociation performance for benzene gas it is effective to form anatase and brookite phases compositely in TiO$_{2}$.

• Applied Chemistry for Engineering
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• v.16 no.6
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• pp.785-789
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• 2005

$TiO_2$ powders with rutile and brookite phases were synthesized through homogeneous precipitation of the aqueous $TiOCl_2$ solution, prepared from $TiCl_4$ and HCl solution, and their properties were characterized. Based on the analytical results appropriate molar ratios of ${Cl^-}_{total}:Ti^{+4}$ in precipitating solution for synthesis of pure rutile phase and a mixture of rutile and brookite phases were proposed. The volumetric proportion of brookite increased with increasing HCl concentration under a typical condition obtaining mixed phase of rutile and brookite. The brookite phase in the mixture was transformed to anatase phase by heat treatment at about $800^{\circ}C{\sim}850^{\circ}C$, and finally converted to rutile phase at $1000^{\circ}C$.

• Applied Chemistry for Engineering
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• v.18 no.6
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• pp.545-551
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• 2007

HCl concentration, reaction temperature, and $Ti^{4+}$ concentration are the decisive factors in determining the structure of precipitates in the process of synthesis of $TiO_2$ particles from aqueous $TiCl_4$ solution by precipitation and the volumetric proportion of brookite phase in $TiO_2$ particles can be controlled by these factors. Pure brookite-type $TiO_2$ nanoparticles were synthesized by heating the aqueous $TiCl_4$ solution with no more than 1.0 M of $Ti^{4+}$, in which the concentration of HCl was kept in the range of about 2.53~6.41 M during reaction, at the temperature below $70^{\circ}C$ for 20 h. Also, Pure brookite was finally transformed to a rutile phase via an anatase phase through heat-treatment.

• Applied Microscopy
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• v.29 no.1
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• pp.95-103
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• 1999

Microstructural observations on the pseudo-brookite $MgTi_2O_5$ and the similar type of $(In_{0.36}Zn_{1.09})Ti_2O_{5.64}$ were carried out using a top-entry HRTEM working at 200 kV. The modulated structures were found in $(In_{0.36}Zn_{1.09})Ti_2O_{5.64}$, however, not in $MgTi_2O_5$. The electron diffraction patterns of sublattice in $(In_{0.36}Zn_{1.09})Ti_2O_{5.64}$ are quite similar to those of pseudo-brookite $MgTi_2O_5$. but the complicated superlattice reflections are present in the diffraction patterns. Four types of modulations have been found. The periodicities for the modulated structure are found to be 3.63 nm, 0.79 nm and 0.64 nm along [220] direction, and 0.81 nm along [420] direction. The phase transition from the modulated structure to the unmodulated one was also observed in situ due to the electron beam irradiation reversibly. Further damage by the electron beam made the crystal to be fragmented into many small crystals with the formation of the voids at the kinks in ledged structure of the surface. The anisotropic arrangements of In and O atoms in $(In_{0.36}Zn_{1.09})Ti_2O_{5.64}$ might cause the compound to be unstable under the electron beam.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.05a
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• pp.117-120
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• 2006

$TiOCl_2$를 중화시키고 과산화수소와 반응시켜 Ti peroxo 전구체를 수열합성법을 이용하여 autoclave 반응기 내에서 가열하여 $TiO_2$ 졸을 제조하였다. Autoclave 반응기 내에 압력을 가하면 브룩카이트상 $TiO_2$졸이 형성됨을 확인하였고, 중화과정에서 NaCl을 첨가하여 Ti 수산화물 격자 내에 Na 이온을 포획되어 브룩카이트상이 나타남을 알 수 있었다. Na 이온의 첨가량에 따라 브룩카이트 결정상 함량이 달라져 광촉매 활성도 달라짐을 브룩카이트상 $TiO_2$가 코팅된 박막의 기상벤젠 광분해 실험을 통해 확인하였고 미세구조, 결정성, 광흡수도률 측정하여 특성평가를 실시하였다.

• Journal of the Korean institute of surface engineering
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• v.40 no.4
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• pp.190-196
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• 2007

Dye sensitized solar cells(DSSC) are the most promising future energy resource due to their high energy efficiency, low production cost, and simple manufacturing process. But one problem in DSSC is short life time compared to silicon solar cells. This problem occurred from photocatalytic degradation of dye material by nanometer sized $TiO_2$ particles. To prevent dye degradation as well as to increase its life time, the transparent coating film is needed for UV blocking. In this study, we synthesized nanometer sized $TiO_2$ particles in sols by increasing its internal pressure up to 200 bar in autoclave at $120^{\circ}C$ for 10 hrs. The synthesized $TiO_2$ sols were all formed with brookite phase and their particle size was several nm to 30 nm. Synthesized $TiO_2$ sols were coated on the backside of fluorine doped tin oxide(FTO) glass by ink jet printing method. With increasing coating thickness by repeated ink jet coating, the absorbance of UV region (under 400 nm) also increases reasonably. Decomposition test of titania powders dispersed in 0.1 mM amaranth solution covered with $TiO_2$ coating glass shows more stable dye properties under UV irradiation, compared to that with as-received FTO glass.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.11a
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• pp.32-32
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• 2003

최근 환경오염에 대한 문제가 심각해지면서 인체에 유해한 유기물질의 분해에 대한 관심이 높아지고 있으며 따라서 뛰어난 광촉매 특성을 보이는 타이태니아(TiO$_2$)에 대한 많은 연구가 수행되고있다. 타이태니아가 보이는 결정상 중에는 brookite, anatse, rutile이 있는데 이 중에서 anatse 상이 가장 우수한 광촉매 특성을 나타내는 것으로 알려져 있다. 그러나 anatse 상을 얻기 위해서는 $600^{\circ}C$ 이상의 온도로 열처리를 해야 한다는 문제점이 있으며 광촉매 특성을 향상시키기 위해서는 anantase 나노결정을 제조하여 표면적을 극대화시 키는 것이 요구되고 있다. 본 연구에서는 이러 한 두 가지 문제점을 해결하기 위하여 Polyethylen oxide(PEO)-TiO$_2$ 나노하이브리드를 Sol-Gel공정을 이용하여 합성하였으며 이들에 대한 hot-water treatment를 통하여 10$0^{\circ}C$ 이하의 저온에서 anatase 나노결정상의 분말을 합성하는데 성공하였다. 이는 SiO$_2$-TiO$_2$계 하이브리드에서만 hot-water treatment를 통하여 anatase로 결정화가 가능하다는 기존의 연구결과와 상반되는 결과로서 무기질 성분으로서 TiO$_2$만 존재하는 하이브리드에 대한 hoi-water treatment를 통하여 anatase결정상이 형성될 수 있었다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.511-511
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• 2007

Low-emissivity (low-e) coatings with visible transparency have attracted increased interest m reducing heat radiation loss through window panes from ecological and sustainable aspects. $TiO_2$-silver transparent thin films for low-e have good properties for UV and IR blocking as well as photocatalyst compared to that with commercial UV blocking films such as fluorine doped oxide (FTO), antimony doped tin oxide (ATO), etc. In this study, transparent $TiO_2$-silver thin films were prepared by successive ink-jet printing of commercial nano silver and $TiO_2$ sol. The $TiO_2$ sol, as ink for ink-jet printing, were synthesized by hydrothermal process in the autoclave externally pressurized with $N_2$ gas of 200 bar at $120^{\circ}C$ for 10 hrs. The synthesized $TiO_2$ sols were all formed with brookite phase and their particle size was several to 30 nm. At first nano sized silver sol was coated on glass substrate, after that $TiO_2$ sol was coated by ink-jet printing. With increasing coating thickness of $TiO_2$-silver multilayer by repeated ink-jet coating, the absorbance of UV region (under 400nm) and IR region (over 700nm) also increase reasonably, compared to that with commercial UV blocking films.